To assist the discharge of material from pneumatic conveying vessels and to the final delivery point gas is fed into various points on a vessel through a distribution manifold. From test data and knowledge the gas split through the manifold can be calculated.
Orifice plates are used to control the flow of gas through the gas distribution manifold. The number and size of holes required in the orifice plate can be calculated using real life data and using the following mathematical calculation: the gas flow (volume/time); the area of the orifice (area) and the velocity of the gas (distance/time).
The calculation gives the theoretical area and therefore the size and number of holes necessary to convey the material. Often, during commissioning, adjustments have to be made to the air distribution through the manifold to get the material to convey. This is achieved by altering the number of holes in the orifice plate.
Changing the number of holes in the orifice plate is usually done by drilling additional holes in a steel plate or welding over the existing holes to reduce the number of holes. As the pneumatic conveying vessels are situated in process plants any work on the system has to be carried out under a permit to work and any modifications carried out in a workshop that could be on the other side of the plant to the vessel. To modify the prior art devices is therefore time consuming and requires specialist tools.
Prior art devices which use adjustable flow control methods often use a single hole with a restrictor of some kind e.g. needle or moveable plug. Again such devices have disadvantages.
It is an object of at least one aspect of the present invention to obviate or mitigate at least one or more of the aforementioned problems.
It is a further object of at least one aspect of the present invention to provide an improved orifice plate for assisting the discharge of material from a pneumatic conveying apparatus.